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<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      /*       var myname ;
        myname = "bozai"

        console.log(myname);
        
        var age = 16 
        console.log(age);
         */

      //  var myname = '静波',
      //  age = 17 ,
      //   sex = '变形人';
      //  console.log(myname, age,  sex);

      // //  console.log(a);  //Uncaught ReferenceError: a is not defined

      //  var b ;
      // //  console.log(b); //undefined

      //  console.log(Number.MAX_VALUE);
      //  console.log(Number.MIN_VALUE);
      //  console.log(Number.MIN_SAFE_INTEGER);
      //  console.log(Math.PI);

      //   var a = 122;
      //   console.log(isNaN(a));
      //   var b = "122";
      //   console.log(isNaN(b));
      //   var c = " nihao";
      //   console.log(isNaN(c));

      //   var d = " 今天 ' 不开车";
      //   console.log(d);

      //   var e = " 今天 \n 不开车";
      //   console.log(e);

      //   var f = "12";
      //   var g = 12;
      //   var h = 12;
      //   console.log(f + g);
      //   console.log(h + g);
      //   console.log(h + g ,f.length);

      // var flag = true
      // var flag1 = false
      // console.log(flag + 1 );
      // console.log(flag1 + 1 );

      // var i ;
      // console.log(i);

      // console.log( i  +  'nihao');

      // console.log( i  + true);

      // console.log( i  +  14 );

      // var j = 'kk';

      // console.log(j);

      // var j = null

      // console.log(j);

      var str = "nihao";
      var num = 12;
      var flag = true;
      var t;
      var kk = null;

      // console.log(typeof str);
      // console.log(typeof num);
      // console.log(typeof flag);
      // console.log(typeof t);
      // console.log(typeof kk);



      // console.log(num.toString);
      // console.log(flag.toString);
      // console.log(t.toString);  //TypeError: Cannot read property 'toString' of undefined
      
      // console.log(kk.toString);  //TypeError: Cannot read property 'toString' of null

    /*   console.log(String(str));
      console.log(String(num));
      console.log(String(flag));
      console.log(String(t));
      console.log(String(kk));
 */
      // 变量 + ''

      console.log(str + '');
      console.log(num + '');
      console.log(flag + '');
      console.log(t + '');
      console.log(kk + '');



    
   

    </script>
  </body>
</html>
